We have been and are doing development and research on construction AI system based on Actor- Critic framework. This paper discusses cyber agents who are computerized agents of mobile entities, which are composed of construction machines, vehicles and workers. Each of the cyber agents would carry with simple function to work together in the Actor-Critic cyberspace. The cyber agents will passively or actively walk through the cyberspace to help for workers to explore and capture critical factors latent in a large amount of information that might go into making decisions. The contents described in this paper might be almost a sublimation of the papers we have submitted to the ISARC for the past decade. This paper is organized as follows. First, this paper describes Actor-Critic framework for construction AI system. Secondly, this paper reports role of cyber agent. Thirdly, this paper explains inference mechanism of abduction reasoning and briefly shows example of inference. Finally, this paper presents further development and research on functions that the cyber agent should carry with in future.